The carbochlorination of refractory, zirconium-containing ores such as zircon (ZrSiO.sub.4) inevitably generates inside the chlorination reactor a normally unreactive residue, which builds up to slowly fill the reactor. This material must be periodically removed, interrupting production. Furthermore, once removed, this material is radioactive due to involatile, naturally-occurring radionuclides such as radium and thorium. Therefore, it must be stored, handled and disposed of as radioactive waste. Such measures are costly. Also, the largest fraction of the residue is unreacted carbon, which is by itself an innocuous material, which can still have chemical reduction and energy values. In present practice, a large amount of costly waste disposal volume is taken up by this carbon.